Diagnosing the performance or mis-performance of an internal combustion engine often requires a technician to monitor the performance of each spark plug in that engine. However, the modern internal combustion engine has been transformed from a basically mechanical device into one that is significantly technologically advanced. Additionally, one of the most effective methods of diagnosing a problem within an internal combustion engine is to analyze the waveform of the voltage that is carried through the electrical circuit attached to the spark plugs. However, it is becoming exceedingly difficult to access this circuit without significant time and expenditure. For example, more modern internal combustion engine ignition systems incorporate an ignition module (ignition switching device) into the ignition coil assembly, which makes accessing the primary winding on the ignition coil impossible. Additionally, the voltage on the secondary winding side of the ignition coil can reach extremely high values (e.g. 65,000 V), making it not only unsafe to attempt to access these voltages, but would instantaneously destroy any conventional oscilloscope if connected without the use of specialized and expensive adaptors.
While observing and analyzing the waveform of the electrical impulse which is directed at each spark plug is useful in identifying many of the problems within an internal combustion engine, it may also be desirable to short or disable a single spark plug within the engine in order to diagnose a weak cylinder. The traditional method of identifying a weak cylinder is to disable one spark plug at a time while an engine is idling. If a cylinder is disabled by disabling the spark plug, and there is no corresponding change in idling speed, the weak cylinder has been identified. However, in many of the newer ignition systems, the spark plug is often recessed into the engine head, preventing access to the plug itself without undue labor and expense.
Thus, what is needed is a safe and cost effective way of both monitoring the performance of a spark plug within an ignition circuit while having the capability to disable that spark plug for further diagnosis.
There have been previous attempts to solve this problem. For example, U.S. Pat. No. 5,933,009 to Kayser discloses a spark plug engine analyzing device and method. Kayser essentially attempts to overcome the problems addressed above by inserting two resistors, having a resistance ratio of 1000 to 1, along the electrical path of the high voltage said of the secondary winding. This will effectively reduce the voltage by a factor of 1000. This voltage is then inputted into a solid state device whose output is a processed waveform which can be displayed on an oscilloscope. The disadvantage of the invention of Kayser is the need to process the reduced voltage signal with a network of resistors and capacitors called a compensated voltage divider before the waveform can be displayed by an oscilloscope. The required processing, wherein half of the signals communicated to the processor are inverted, not only requires two output channels such that all of the signals from the circuit can be observed, but also eliminates the possibility of all of the signals being viewed simultaneously on one oscilloscope or other observation device. In addition, by virtue of the fact that the device of Kayser is not grounded to the vehicle, it would be impossible for the device to short a spark plug.
Another attempt at solving the foregoing problem is disclosed in U.S. Pat. No. 6,426,626 to Kravis. However, this device is limited to analyzing problems within a spark plug or ignition coil itself. In the invention of Kravis, an external power source is used to supply power to an engine's ignition coil. Because an external power source is used without an operating engine, it cannot be used to analyze any problems associated with an operating engine, such as air fuel mixture problems, pre-ignition problems, misfire problems, power train control module problems, ignition wire problems etc. Furthermore, there is no method disclosed for disabling a spark plug.
Therefore what is needed is a device and method for both analyzing the waveform of an spark plug circuit on the high voltage side of an ignition coil which can display the waveform without solid state processing, which can alter the waveform, or can alternatively disable, or short, individual spark plugs.